Scala-链接两个隐式转换时如何模式匹配？ [英] Scala - how to pattern match when chaining two implicit conversions?

问题描述

我编写了一种解析Metrics数据的方法，首先遇到了transactionMap类型的问题，该类型是 java.util.Map 。我使用JavaConverters解决了它。

I wrote a method to parse Metrics data and at first faced a problem with the type of transactionMap which is a java.util.Map. And I solved it using JavaConverters.

def parseMetrics(metric: Metric) = {
    import scala.collection.JavaConverters._
    metric.transactionMap.asScala.values.map {
      case false => "N" 
      case true => "Y"
    }.toList

但是此后在模式匹配为真时出现错误和错误值：模式类型与预期类型不兼容，发现：布尔值，必需：java.lang.Boolean

But after that I got an error while pattern matching true and false values: pattern type is incompatible with expected type, found: Boolean, required: java.lang.Boolean

据我了解，Scala没有链接两个隐式转换。有没有办法使用JavaConverters修复它？

As far as I understand Scala does not chain two implicit conversions. Is there a way to fix it using JavaConverters?

推荐答案

使用if / else而不是match语句进行布尔检查：

Use if/else rather than a match statement for Boolean checking:

def parseMetrics(metric: Metric) = {
    import scala.collection.JavaConverters._
    metric.transactionMap.asScala.values.map {
      x => if (x) "Y" else "N"
    }.toList

我的怀疑是在if语句中，可以将 java.lang.Boolean （我在这里假定为 x ）强制为 Boolean 通过 import scala.collection.JavaConverters ._ ...但match语句不会执行相同的强制，但必须显式进行（或匹配 java.lang.Boolean 值）。

My suspicion is that within the if statement the java.lang.Boolean (which I presume x is here) can be coerced to Boolean via import scala.collection.JavaConverters._... but the match statement doesn't do the same coercion, but would have to be made explicitly (or match on the java.lang.Boolean values).

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